1. Technical Field
The present disclosure relates to a method for computing color correction parameters for use in color correction to image information such as image signals output from an image capture device.
2. Description of the Related Art
It is a common practice to capture an image of an object using an image capture device, such as a digital camera (digital still camera or digital video camera) or a scanner, and display the captured image using a display device such as a display or a projector. For example, a certain scene can be photographed with a digital camera and the image of the scene can be displayed on a display. In such a situation, colors that are perceived in the real scene typically do not match colors perceived from the scene reproduced on the display even if the digital camera and the display adhere to the same standard for color space. More specifically, when a certain color is considered, the color coordinate values in the real scene do not agree in a color space with the color coordinate values reproduced on a display. The characteristics of an optical system including lenses, color filters, and an image sensor vary from one image capture device to another. Thus, the degree of such inconsistency of colors varies depending on the image capture device used for photographing the scene.
In view of these circumstances, color correction is usually applied to image signals or image data obtained by an image capture device. As an example, a technique is known that approximates the colors of a color image being reproduced to the original colors through a color correction process using a color conversion matrix (Japanese Unexamined Patent Application Publication No. 2005-45446). The technique according to Japanese Unexamined Patent Application Publication No. 2005-45446 determines such a color conversion matrix that reduces the color difference calculated using the L*, a*, and b* components of the target color and the L*, a*, and b* components of a corrected color in CIE 1976 L*a*b* color space (hereinafter sometimes referred to as “CIE-L*a*b* color space”) by iterative solution of the least squares method. A unit matrix is used as the initial value in optimization of the color conversion matrix. In the color conversion matrix computation method described in Japanese Unexamined Patent Application Publication No. 2010-124168, only a* and b* out of the L*, a*, and b* components are used to perform iterative solution of the least squares method in optimization of the color conversion matrix, thereby reducing the computational load. Japanese Unexamined Patent Application Publication No. 2010-124168 also proposes using a matrix that gives exact corrected values for randomly selected three colors as the initial value in place of a unit matrix so that the color conversion matrix can be optimized with a reduced computational load.